Now back to fort hood and the latest on a shooting spree that left three soldiers dead and 16 wounded. This Wednesday, a memorial service will be held on post. Meanwhile, investigators are trying to figure out why one soldier went on a rampage. ABC's Pierre Thomas has been tracking that part of the story. Pierre. Reporter: Good morning. It increasingly appears this deadly shooting spree was done by a soldier with mental health issues who may have had a simmering resentment toward the army. A simple argument. That's all it may have taken to ignite a hail of gunfire that left three soldiers murdered and 16 others wounded. We believe that the immediate precipitating factor was more likely an escalating argument in his unit area. Reporter: Possible source of that dispute, Wednesday Iraq war veteran Ivan Lowe possepez was applying for leave and frustrated by a slow-moving bureaucracy. He was told to come back tomorrow. Reporter: And we were told about his son, Jonathan's, near-fatal encounter with the suspect. He left the office and reappeared with a gun. Then the shooting began. From what I was told, the first person that was hit died, and then the gun was turned on my son. And he was hit four times. Reporter: Lopez allegedly went on a shooting spree, opening fire in two buildings. And from his car while driving on the base. ABC news learned the suspect fired dozens of shots before he killed himself. But why would Lopez be so angry about a slow response to a request for time off? His family in Puerto Rico tells ABC news that he had been frustrated that the military only gave him limited time to go home when his mother died of a heart attack last November. Sources tell ABC news that frustration 2009ed with lingering mental health issues was apparently a lethal mix. He was undergoing a variety of treatment and diagnosis for mental health, ranging from depression and anxiety to sleep disturbance. He was prescribed a number of drugs to address those. Reporter: The FBI and the military continue to dissect his life to better understand his state of mind. A frustrated source told me last night a simple disagreement shouldn't spark such a violent outburst. It doesn't make sense. We need to know more. Thanks, Pierre. So many questions about what caused this. Was it related to any of the experiences overseas in the military? The struggles soldiers face when returning home is an issue I have been covering for years. After well over a decade of fighting overseas, the once-invisible wounds of war are following service members home. The Numbers are staggering. With over 130,000 Iraq and Afghanistan veterans treated for PTSD last year alone. But post-traumatic stress rarely leads to violence. Depression, anxiety, PTSD, those are on the mild end of the scale. When we have violence associated with mental illness, it's usually people with delusions, paranoia, psychosis. But a new survey of Iraq and Afghanistan war veterans shows four in ten say they have experienced outfirsts of anger related to their military service. And more than half say they have felt disconnected from civilian life. And an epidemic of suicides has the military's top leaders promising help. We can better share information so that the -- the chain of command, as you have said, has the ability to really understand when soldiers are having problems. But even awareness can't prevent tragedy. Back in 2009, ABC news visited this combat stress center in Baghdad, set up to aid soldiers suffering from the strains of war. The great thing is to have a leader bring in a soldier, come in leadership staff and come in and ask us to that we can help them take care of their soldiers. But just days later, one of those soldiers turned his weapon on his comrades, killing five. This week's shooting at fort hood, serving as a tragic reminder that even with resources in place, such violent acts can be difficult to prevent. What should they do? The army has to take a knee and look within itself and focus intensely on taking care of the people it has and give them the resources they need to truly come home from war.

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